In youth, loss of control (LOC) eating is associated with increased eating pathology and general psychosocial problems and psychological symptoms,1-6 and is predictive of excess weight gain7 and worsening eating pathology including full syndrome binge eating disorder.8 Rates of LOC eating among adolescent girls are high,9, 10 especially among treatment-seeking samples in which prevalence estimates are around 30%.2, 11, 12 Despite its adverse correlates, little is known about the etiology of LOC eating, specifically, the moment-to- moment processes that promote LOC. One model hypothesized to explain LOC eating is the Interpersonal Model, which posits that interpersonal problems precede and predict negative effect, which in turn precedes and predicts episodes of LOC eating.13 Many studies of LOC to date rely on self-report or laboratory assessment strategies, which are limited by the need for participants to summarize behaviors over weeks or months, or which may not reflect behavior in the natural environment. The present study aims to extend upon knowledge from existing research by using ambulatory monitoring to examine the validity of the Interpersonal Model of LOC in girls' naturalistic settings. Using electronic digital palm top computers, girls with LOC will be queried regarding their interactions and relationships, mood, and eating episodes, as they occur throughout the day, for a period of two weeks. Because data suggest that inability to identify and report emotions may be especially salient among individuals with disordered eating, affect will be dually measured by self-report and heart rate variability. Specific Aims of the current study include the following: Aim One: To test the feasibility of examining the Interpersonal Model of LOC eating in an ecologically valid and temporally sensitive manner using ambulatory monitoring. Aim Two: To evaluate momentary associations between self-reported negative affect and heart rate variability. Aim Three: To evaluate the validity of the Interpersonal Model which hypothesizes that interpersonal problems precede and predict negative affect and that negative affect precedes and predicts episodes of LOC eating. Participants will be 30 overweight adolescent girls who report episodes of LOC eating in the month prior to assessment. Subjective-reports of girls' interactions and relationships, mood, and eating episodes will be collected at stratified intervals throughout the day for two weeks using digital palm top computers. Heart rate variability will be concurrently monitored for two days. Results will illuminate psychosocial and physiological mechanisms that may accompany or predict LOC eating, which has potential to reduce the emergence of binge eating or eating pathology throughout development.